The present invention is directed to a plug part for releasable plug connection of light waveguides wherein the plug part includes a cylindrical carrier tube in which an optical fiber is centrally fixed and the end surface of the part and the fiber are planarly processed to extend perpendicular to the axis of the carrier tube.
A plug part having a fiber disposed on an axis of a carrier tube with the end of the fiber and tube being planarly processed to lie in a plane perpendicular to the axis of the carrier tube is disclosed in German Patent No. 25 16 858. In the plug part disclosed in this patent, the optical fiber is freed of its cladding in its end region and is introduced into the bore of a cylindrical carrier tube where it is centrally fixed by gluing. Subsequently, the fiber end together with the end face of the carrier tube are ground and polished so that a planar end face arises which should be aligned as precisely as possible perpendicular to the outside diameter of the carrier tube and to the axis of the tube. For producing a plug connection two of these plug parts are introduced into a precisely fitting common sleeve and their end faces are pressed against one another either by a spring or through a screw or threaded fitting. As a result of this axial pressing, the end faces should lie flat against one another whereby a beam reflection is to be particularly prevented.
In the known plug connections, the axial plugging forces are absorbed by the optical fibers at least to a considerable degree. A dislocation of the optical fibers in the carrier tube can occur on the basis of these mechanical stresses. Particularly, given the thermal cycling, the adhesive layer surrounding the optical fiber begins to work and becomes displaced to extend beyond the end face of the plug. A disturbing reflection will occur due to an air gap which is produced between the two plug parts of the plug connection by this flow of the adhesive.
German AS No. 26 52 712 discloses a releasable plug connection for light waveguides wherein an annular distancing or spacing washer is inserted between the end faces of the carrier tubes of the two plug parts. This spacing washer is a precisely defined spacing between the end faces of the optical fibers so that no optical reflection can occur in this connected segment. The defined spacing would thus have to be adapted via the thickness of the annular spacing washer to a fraction of the wavelength .lambda. of the light to be conducted and this is not practically implemented with known machining processes.
In German AS No. 19 53 283, an arrangement is also disclosed in which an annular spacing or distancing washer is inserted between the end faces of the carrier tubes of both plug parts in a releasable plug connection of light waveguides. According to one alternative, however, it should also be possible to achieve a precisely defined space between the end faces of the optical fibers in that the transmitted optical energy is set to its maximum value with the assistance of a mounting and adjustment device. The mounting and adjustment device, which guarantees such a precise definition of the interferometer length, however, are not available in practice.